Introduction Cardiac CT, incorporating coronary artery calcium (CAC) scoring and angiography, is being increasingly used to evaluate patients with chest pain and exclude coronary artery disease (CAD), as recommended in the recent NICE guidelines. Calcification of the coronary arteries is an excellent marker of underlying atherosclerosis, but a zero CAC score does not completely exclude the diagnosis as potentially significant non-calcified plaques will not be detected by CAC scoring. CT imaging may also identify non-cardiac incidental findings that can lead to further downstream testing and medical expense.

Objectives (1) To evaluate the probability of CAD in patients with a CAC score of zero. (2) To determine the incidence of non-cardiac incidental findings on cardiac CT and to quantify resulting investigations.

Methods 116 symptomatic patients undergoing cardiac CT to exclude CAD from November 2009 to October 2010 were prospectively enrolled. Patients underwent CAC scoring and had contrast-enhanced, 128-slice, dual source CT coronary angiography (CTCA―Siemens Flash). Scans were dual-reported by a cardiac radiologist and a cardiologist. Statistical analysis was performed using GraphPadPrism.

Results 62/116 patients had a CAC score of zero. Of these, 57 (91.9%) patients had normal coronary arteries, 4 (6.5%) patients had non-obstructive CAD (stenosis <50%), and 1 patient (1.6%) had significant obstructive CAD (stenosis>50%). This patient with obstructive CAD had a high grade lesion in the proximal left anterior descending artery that required intervention. 54/116 had non-zero CAC scores. Of these, 13 (24%) had obstructive CAD and 41 (76%) non-obstructive CAD. 42/116 (36%) patients had incidental findings on cardiac CT that are summarised in Abstract 111 table 1. These incidental findings resulted in further investigations, documented in Abstract 111 table 2. The mean radiation dose (± SEM) for CAC scoring was 0.61±0.03 mSv. The mean radiation dose (± SEM) for subsequent CTCA was 2.66 ± 0.32 mSv in high pitch “flash” mode (n=27), 5.86±0.50 mSv in prospective mode (n=64) and 17.15±1.68 mSv in the retrospective mode (n=25).

Conclusions Despite 62 patients having a reassuring CAC score of zero, 8% of this group had evidence of non-calcified plaque, with one patient having obstructive CAD that required intervention. We conclude that if strong clinical suspicion remains in patients with a CAC score of zero further coronary investigation may be warranted. Incidental findings are common, and can result in multiple further investigations for patients. Further research is needed to evaluate the added cost, clinical benefits and radiation exposure created by investigation of such incidental findings in the context of cardiac CT.